The present invention relates to a method and apparatus for applying decorative imprints to articles, particularly printing a design with a silk screen having a resilient membrane connected between the screen and a silkscreen support frame.
As is well known in the art, a squeegee is passed across the surface of a stencil screen to force a printing medium through the screen for imprinting a desired design defined by pervious openings in the screen. The printing medium for the imprint may be solvent-based paint or thermally-responsive paint. When thermally-responsive paint is used, it is heated prior to being poured onto the stencil screen where it is forced through an opening in a paint-impervious screen by the squeegee. For successful operation of this process, it is necessary to pass an electric current through the metallic mesh forming the screen so as to heat the same and prevent premature hardening of the thermally-responsive paint.
In my U.S. Pat. No. 4,137,842, there is disclosed a silk-screen printing method and apparatus in which the surface of a silk screen which is brought into contact with the workpiece is coated with a silicone-release agent. A solvent is passed through openings in the wire mesh to remove the coating material from the paint-pervious openings in the screen. The silicone-release agent prevents sticking of the heated screen when brought into contact with the surface of a polyethylene workpiece.
A silk screen is typically comprised of wire mesh stretched between edges of a frame so that end portions of the wire mesh can be wrapped to extend along the sides of the frame and secured thereto. The screen is usually stretched with sufficient tension to eliminate wrinkles and prevent distortions of the desired pattern which is located in a central area of the screen surrounded by the sides of the frame. Sometimes the frame is moved along a path of travel relative to a stationary squeegee to force ink through the paint-pervious openings in the screen; however other drives for the printing process provide that the squeegee moves along a path of travel relative to the screen. In either printing process, the screen is stretched by the squeegee to a small extent each time the printing medium is forced through the paint-pervious openings by the squeegee. After a period of use, the metal or other material used to form the screen fatigues and a tear occurs in the screen. The screen must, therefore, be replaced and usually the entire screen assembly is replaced on the printing machine. The fatigue life of the screen material can be enhanced by attaching a gasket to the lower edge surface of the frame to avoid stretching of the screen across a sharp edge of the frame. However, fatiguing of the screen material still occurs because the screen must be pressed into contact with the workpiece by movement of the squeegee along the screen. The screen is normally positioned a short distance from the surface of the workpiece so that an airgap exists between the screen and the workpiece. The squeegee is moved to displace the screen by the distance of the airgap into contact with the workpiece.